1. Field of the Invention
This invention relates to an antenna element for realizing equivalent gain for plural frequencies and to a radio apparatus applicable to plural radio communication systems having different frequency domains by having this antenna element mounted thereon.
2. Description of Related Art
In a radio communication system, such as a portable telephone system, which has come into surprisingly widespread use, not only call services but also transmission services for transmission of text information, such as E-mail. In the portable telephone system, downloading services for received melodies or character distributing services have met high acclamation. In the portable telephone system, a wide variety of measures are being taken to transmit the various forms of the information more speedily and at a higher quality. In near future, high quality moving picture information will also be transmitted in real-time.
As a new system to cope with high transmission speed in inland use, services conforming to IMT-2000 (International Mobile Telecommunication-2000) are scheduled to be started in the field of the portable telephone system. In this system, services can be furnished for the time being at a rate of 384 kbits/sec, against 64 kbits/sec of the pre-existing system, as a result of allocation of a new frequency band (2 GHz band). In the portable telephone system, a need exists for an equipment that enables various information signals to be received in this new frequency band.
In each radio communication system, the frequency band is prescribed, such that the limited frequency range needs to be exploited efficiently. The radio communication system needs to be designed so that an equipment exploiting the system will receive only the desired electrical waves while not receiving other electrical waves which prove to be interference, in order to permit the system to be exploited efficiently. In the radio communication system, an adaptive array antenna 100, shown in FIGS. 1 to 3, is mounted on the equipment exploiting the system.
Referring to FIG. 1, the adaptive array antenna 100 includes plural antenna element 101, plural reception circuit units 102 for demodulating high harmonics received by the respective antenna element 101, and a parallel signal processing circuit unit 103 for optimizing the signals optimized by the reception circuit units 102. The adaptive array antenna 100 is adapted for simultaneously receiving high frequency signals oncoming from different directions by the antenna element 101 and for interrupting high frequency interference signals.
The respective reception circuit units 102 down-convert the high frequency signals received by the respective antenna element 101 to demodulate the received signals to bit signals. The parallel signal processing circuit unit 103 optimally synthesizes bit signals supplied from the reception circuit units 102. The adaptive array antenna 100 synthesizes bit signals in the manner of cancelling the information other than the information needed in the parallel signal processing circuit unit 103, and the noise, to operate as if the unit 100 is oriented in alignment with the direction of electrical waves for which antenna directivity is required, while being null with respect to the direction of oncoming of interference electrical waves.
The adaptive array antenna 100 provides plural outputs from the parallel signal processing circuit unit 103, so that, if there are two or more information that are required, the respective information will be output separately. That is, the adaptive array antenna 100 has characteristics such that it operates with plural directivities in meeting with the number of the required information. The adaptive array antenna 100 features enabling reception of plural information employing the same frequency band possibly present in the same space without crosstalk to achieve effective utilization of the frequency band.
The antenna element 101 includes, as shown in FIGS. 2 and 3, a rectangular dielectric substrate 104 of e.g., Teflon (trade name of a product manufactured by DuPont de Nemur), a grounding conductor 105 provided on a first major surface 104a of the dielectric substrate 104, plural radiating conductors 106 bonded to a second major surface 104b of the dielectric substrate 104 and a feeder line 107 interconnecting the grounding conductor 105 and the radiating conductors 106. The dielectric substrate 104 has a specific inductive capacity xcex50 and includes plural feeder guide holes 108 passing through the first major surface 104a and the second major surface 104b, as shown in FIG. 3.
The grounding conductor 105 is a metallic plate of, for example, copper or brass, bonded to the first major surface 104a of the dielectric substrate 104. On the bottom surface of the grounding conductor 105 are arranged the reception circuit units 102. The radiating conductors 106 are bonded to the second major surface 104b of the dielectric substrate 104 kept parallel to the grounding conductor 105. The radiating conductors 106 are formed e.g., by chips of metal, such as copper or brass, each being of a square shape with each side being L in length. The length L of each side of the radiating conductor 106 is xcex/2, where xcex is the wavelength of the wave transmitted/received. The length L of the radiating conductor 106 is also set by
2L=c/(f0xc3x97{square root over (xcex50)})
where f0 is the transmission frequency and c is the light velocity.
The feeder line 107 is a coaxial cable passed through the feeder guide hole 108 to interconnect the radiating conductors 106 and the associated reception circuit units 102. Although not shown in detail, the feeder line 107 has its shell conductor and a core line connected to the grounding conductor 105 and to the radiating conductors 106, respectively.
In the above-mentioned adapter array antenna 100, high frequency signals 109 (109a, 109b, 109c) of the same frequency band, transmitted from different directions, are received by respective antenna element 101, as shown in FIG. 3. In the adapter array antenna 100, the high frequency signals 109 are down-converted in the respective reception circuit units 102 associated with the antenna element 101 for demodulation to bit signals. As shown in FIG. 1, the adapter array antenna 100 synthesizes the bit signals supplied from the respective reception circuit units 102 in the parallel signal processing circuit unit 103 such as to cancel the information other than the information needed in the parallel signal processing circuit unit 103 and noise to output the resulting signal.
In the radio communication system, plural systems employing different frequency bands have come to be furnished, as described above, such that equipment to be used in the system are required to cope with these systems. If the equipment is to be usable in common by the respective radio communication systems, plural antennas adapted to the respective systems are needed, thus being increased in size and cost.
consideration that the portable telephone system has become surprisingly widespread on account of the small size and weight and inexpensiveness of the equipment, it is not possible to permit the portable telephone set to be bulky in size and costly with the introduction of new portable telephone system as described above. So, the new portable telephone system has an inconvenience that a portable telephone set furnished is not compatible with the conventional portable telephone set.
The conventional adaptive array antenna controls the directivity in the same frequency band to enable effective frequency utilization. If this adaptive array antenna is to be applied to plural systems having different frequency bands, plural antenna adapted to the specifications of the respective systems need to be used, as in other types of the antenna.
It is therefore an object of the present invention to provide an antenna and a radio apparatus which, in view of the above-described characteristics of the adaptive array antenna, the necessary information can be positively received in plural frequency bands to achieve effective frequency utilization.
In one aspect, the present invention provides a antenna element including a substrate formed of a dielectric material having a specific inductive capacity exhibiting frequency distributing properties, a grounding conductor formed on one surface of the substrate, a plurality of radiating conductors formed on the other surface of the substrate and a plurality of feeder lines provided for passing through the substrate for connecting the grounding conductor to the radiating conductors.
With the antenna element of the present invention, in which the substrate is formed of a dielectric material having frequency distribution characteristics, an equivalent gain may be achieved for plural frequencies.
In another aspect, the present invention provides an adaptive antenna apparatus including a substrate formed of a dielectric material having a specific inductive capacity exhibiting frequency distributing properties, a grounding conductor formed on one surface of the substrate, a plurality of radiating conductors formed on the other surface of the substrate, a plurality of feeder lines provided for passing through the substrate for connecting the grounding conductor to the radiating conductors, a frequency distributing circuit fed with a reception signal of a plurality of frequency bands from the radiating conductors over the feeder line for outputting signals of the frequency bands in the reception signal in separate frequency bands, a plurality of demodulation circuits for demodulating the signals of the respective frequency bands from the frequency distributing circuit, and a signal synthesis circuit for synthesizing demodulated signals from the demodulating circuits according to the separate frequency bands.
With the adaptive antenna apparatus of the present invention, plural information transmitted from plural systems with different frequency bands can be received without crosstalk by a sole antenna device so that it is possible to reduce the size of the device.